Process and apparatus for accelerating crystal growth



March 22, 1960 H. J. c. GEORGE 2,929,692

PROCESS ANDIAPPARATUS FOR ACCELERATING CRYSTAL GROWTH Filed May 20, 1957 2 Sheets-Sheet 1 Fig. I Q i S $//7 Fig. 2 2

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March 22, 1960 H. J. c. GEORGE PROCESS AND APPARATUS FOR ACCELERATING CRYSTAL GROWTH Filed May 20, 1957 2 Sheets-Sheet 2 Fig. 7

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HENRI GEORGE ATTORNEYS United States Patent PROCESS AND APPARATUS FOR ACCELERATING CRYSTAL GROWTH Henri J. C. George, Paris, France, assignor to Quartz & Silice, S.A., Paris, France, a corporation of France Application May 20, 1957, Serial No. 660,208 Claims priority, application France June 1, 1956 14 Claims. (Cl. 23-301) The present invention relates to an improved process and apparatus for accelerating the growth of monocrystals of large dimensions from solutions of the substance.

It is known that the manufacture of monocrystals is accomplished by growing from a crystalline seed placed in a super-saturated solution of the substance, the salt depositing itself on the crystal seed because of the supersaturation of the mother liquor. One may obtain the super-saturated solution either by varying the temperature of the solution (if the solubility of the salt varies with temperature), or by adding salt to the solution, or by evaporating solvent.

The preparation of monocrystals of large dimensions, free from defects such as snow, inclusions of liquid or impurities in the crystal, twin crystallization or defects in the lattice, etc. presents multiple diificulties because crystallization primarily depends upon one or more factors, such for example, as the following: sufficient replenishing of the enriched or nourishing solution; elimination of impoverished solution; neutralization or compensation of thermal phenomena (either the absorption or the giving of heat) which accompanies crystallization.

Moreover, in the process heretofore practiced, because of the great number of precautions which must be observed, the growth of a monocrystal has always been very slow and requires days, sometimes even months, before the dimensions reached are sufiicient for industrial use of the monocrystal.

The object of the present invention is to provide a process and apparatus for accelerating the growth of monocrystals which are free from the faults listed above.

In accordance with the invention several points adjacent to the face of the crystal to be grown are nourished with a saturated solution, while at the same time the impoverished or unsaturated solution is eliminated. The preferred procedure for carrying out the process comprises the nourishing of the growing face by directing jets of a saturated solution substantially perpendicular to the said face, which jets after impinging the crystal face spread out, meet one another, and merge to form return jets of impoverished solution which is removed by aspiration. The invention also provides means for oscillating the jets parallel to the face or faces of the crystal under treatment so that the entire area of each face is swept by the jets.

In accordance with the invention the simultaneous growth of several faces of one crystal may be achieved with speeds of growth which may vary. In such case the geometrical arrangement of the jets conforms to the polyhedral form corresponding to that of the crystal. The discharge from the jets can be regulated in such a manner that each of the faces will grow with the required speed.

The invention also embraces apparatus for practicing the process, and several examples of these devices are hereinafter shown with reference to the accompanying drawings, wherein:

Fig. l is a section of elementary apparatus for the accelerated growth of monocrystals;

Fig. 2 is a schematic representation of the area of impact of the jets on the face of the crystal under treatment;

Fig. 3 is a section of apparatus for the accelerated growth of monocrystals having its own system of aspiration;

Figs. 4 and 5 are variants of the apparatus shown in Fig. 3;

Fig. 6 is a representation of a monocrystal of ammonium dihydrogen phosphate;

Fig. 7 is a vertical section through an installation employed for the growing of monocrystals of ammonium dihydrogen phosphate and the like salts, and

Fig. 8 is a view in end elevation of the oscillating system.

Referring to Fig. 1, the elementary device shown therein comprises a sprinkler 1 having a wall 2 provided with holes 3 defining spaced nozzles, and these nozzles may, if desired, be extended as hereinafter shown. The sprinkler 1 is disposed approximately 7 mm. in front of the face of the crystal which is to be grown, and is supplied with a solution through an inlet 4 connected with a pump (not shown) which withdraws the nourishing liquid at the proper temperature from a supply reservoir. Each nozzle 3 discharges against the crystal face a jet of nourishing liquid, and the nozzles are arranged in such a manner that the jets impinge substantially perpendicular to the face which is to be grown. As illustrated in Fig. 2, each jet 5 impinges against the face of the crystal 6, then spreads out as indicated at 7 and merges with a neighboring jet to form a reversely directed jet 8 of partially de-saturated or impoverished solution.

In order that the jets of impoverished solution do not disturb the jets coming from the sprinkler 1 the invention provides means designed to aspirate this impoverished solution, as shown in Figs. 3, 4 and 5.

In the embodiment shown in Fig. 3 tubes 13 provide elongate nozzles projecting from sprinkler 11, and these nozzles traverse a chamber 15 having an outlet 10 and a wall 12 formed with openings 14 into which the discharge ends of the nozzle project so as to provide annular inlet passages communicating with the chamber 15. The pressure within the chamber 15 is maintained depressed, being of the order of 50 mm. of mercury, so that the liquid returning from the jets after having impinged on the face of the crystal is aspirated out.

Fig. 4 shows a variation in the device of Fig. 3. In this embodiment the Wall 20 of sprinkler 22 is provided with spaced holes defining nozzles 21 and the sprinkler is traversed by the tubes 23, the outer ends of which fit openings in the wall 20 and their inner ends com municate with a chamber 24 where the pressure is subatmospheric, as in the previously described embodiment. The tubes 23 are evenly spaced throughout the surface of the wall 20, and the nourishing liquid is discharged through nozzles 21 in the form of jets, the impoverished solution being aspirated through the tubes 23 and returned to the chamber 24.

Fig. 5 shows another variation in which the wall 3% of the sprinkler 31 is provided with holes defining nozzles 32 and other blind holes 35 which communicate with conduits 33 bored within the body and parallel to the surface of the wall 30. These conduits 33 are connected through a return manifold 34 to an aspirating device (not shown). As in the case of Fig. 4, the jets of nourishing solution are discharged through the nozzles 32, while the impoverished solution is aspirated through the holes 35 and returned ,through the conduits 33and manifold 34'to the aspirating system.

The invention also includes means forproducing an oscillatory movement of the sprinkler relative to the face of the crystal. to be grown, the purpose of the movement ;,being to avoid defects arising by reason of the fact that the area on the face ofthe crystal to be grown at the junction-f the two liquid sheets spreading out'from the neighboring jets comprises a zone that is less nourished.

This displacement or oscillation of the sprinkler has an amplitude at least equal to the space between the two essence 'a crystalline structure. A crystal of ammonium dihydrogen phosphate belongs to the tetragonal system and is constituted by a right prism having a square base 40 and terminates at its two ends by pyramids 41. Preparatory .to growing a selected face on the pyramid 41 a seed 42, delineated by the broken lines of Fig. 6, is first cut parallel to one of the faces of the pyramid 41, for example, the face 44.

7 The sprinkler is disposed opposite the face 44a of the crystalline seed which is to be grown selectively by the feedingof the saturated salt solution. The growth of an adjoining parasitic face parallel to the face 43 of the pyramid 41 can be observed and the growth of this parasitic face is due only to the deposit of salt from thesolution in which the crystal is. bathed, since it is not directly fed by the sprinkler. As this face will grow more slowly. than the face 44a (theface parallel to the face 44 of the original crystal) it reduces thedimension of the latter. In order to avoid the disproportionate growth of the parasitic face there is utilized an auxiliary sprinkler which assures the proper feeding of solution to the parasitic face. A satisfactory apparatus foraccomplishing the proper growth on adjoining faces is shown in Fig. 7.' A crystal is placed in a vessel 51 of a material inert to the solution, and preferably transparent. The vessel 51 is filled with a saturated solution of ammonium dihydrogen phosphate maintained at a temperature of 50 C. 'The principle sprinkler 52, having a construction basically the same as that of Fig. 3, is placed opposite the large face 53 of the crystal 50 and an auxiliary sprinkler 54 of similar construction is placed opposite the face 55 parallel to the face 53. The two sprinklers may be integrally connected and the intakechamber of sprinkler 54'is connected with that of the sprinkler 52 by a suitable duct 49;

The principal sprinkler 52 is fed with a solution which is exactly at the same temperature as the solution of the vessel, that is, 50 C., but the auxiliary sprinkler is fed by a solution a little colder than that of theprincipal sprinkler, that is to say slightly richer in solute. The latter solution is obtained by causing the solution at 50 C. to

pass through a heat exchanger 56 containing water -or coolant regulated to bring about a temperature difierence of about 1 C. r

The sprinklers are made of material inert to ammonium dihydrogen phosphate, preferably a plastic material.

The feeding takes place through a pump 57 and flexible conduits 58 and 59 which are respectively connected to the discharge chambers of the principal and auxiliary sprinklers 52 and 54. Aspiration of the solution takes place through a conduit 60 connected with the outlet of sprinkler 52.

A motor 61 operates an oscillating system 62 of conventional design and construction which acts on the sprinklers to oscillate them parallel to the faces of the crystal under-treatment in such a manner as to assure a sweeping of these faces by the jets discharged from'the nozzles. The oscillating system includes a' radially slotted disc 69 secured to the motor shaft and adjustably receiving a crank pin on the end of a connecting rod 68 pivotally mounted to the end of the crank 67 fixed to the end ofa shaft 66 journalled in a suitable bearing 7 0 secured 'to the wall of the vessel 51. The pressure of the jets, in

the case of ammonium dihydrogen phosphate and under L the conditions described above, is of theorder of several When the described process is used, the rate of growth of the crystals of ammonium dihydrogen phosphate may reach several centimeters per day. I

It shouldtbe understood that this disclosure is for the purpose of illustration'and that variousmodifications in both the process and apparatus maybe made without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. The process for accelerating the growth of monocrystals, which comprises impinging on a selected face of crystal a plurality of spaced nourishing jets'of a saturated solution so that the jets upon striking the crystal face spread out and merge to form a plurality of reversely directed jets of impoverished solution, and aspirating said reversely directed jets, before they interfere with said nourishing jets. I

2. The process set forth in claim 1, wherein said nourishing jets impinge at right angles on the face of the crystal under treatment.

3. The-process set forth in claim 1, wherein said saturated solution consists of an aqueous solution of ammonium dihydrogen phosphate.

4. The process set forth in claim 1, wherein said nourishing jets are simultaneously oscillated so as uniformly to sweep over the entire face of the'crystal under treatment. r

5.- The process set forth in claim 4, wherein amplitude of oscillatory movement is at least equal to the distance between adjacent jets. f 6. The process for accelerating the growth of monocryst'als, which comprises impinging on adjoining faces of a crystal a plurality of spaced jets of a saturated solution so that the jets upon striking the crystal faces spread out and merge to form a plurality of reversely directed jets of impoverished solution, .and aspirating said reversely directed jets before they interfere with said nourishing jets. I t

' 7. The process set forth in claim 6, wherein the crystal under treatment is gradually withdrawn as the growth on said faces continues. v 8. The process set forth in claim 6, whereinthe temperature of one of the nourishing jets directed against one face is less than the temperature of the jets'directed against the adjoining face. 7 j V 9. The process set forth in claim 6, wherein the jets are oscillated in a direction parallel to the crystal faces under posed between said jets for removing reversely directed 'ets of impoverished solution formed after said nourishing jets strike said face, means interconnecting said aspirators, further means for supporting a crystal in fixed position, said means being adjustable to move said crystal in a path parallel to the optical axis of said crystal to maintain the growing face of said crystal parallel to said bank and in properly spaced relation to said discharge nozzles, and means for simultaneously oscillating feed jets and aspirators in a direction parallel to the crystal face.

12. Apparatus set forth in claim 11, wherein the amplitude of oscillation is greater than the spacing between said jet.

13. Apparatus for producing an accelerated crystal growth, comprising means for supporting a crystal in fixed position, two integrally connected sprinklers respectively disposed opposite adjoining faces of a crystal held by the supporting means, each sprinkler having a plurality of nozzles arranged to discharge jets of nourishing solution against one face of the crystal under treatment and a plurality of aspirators interposed between said nozzles for removing reversely directed jets of impoverished solution formed after said jets strike said face, means for oscillating said sprinklers in a direction parallel to the crystal faces under treatment, feed conduits for connecting said nozzles with a supply of solution, and discharge ducts connected with said aspirators,

said means for supporting a crystal being adjustable to move said crystal in a path parallel to an optical axis of said crystal to maintain the growing face of said 'crystal parallel to said sprinklers and in properly spaced rela- References Cited in the file of this patent V UNITED STATES PATENTS 2,042,610 Littleton June 2, 1936 2,080,083 Maginen May 11, 1937 2,724,215 Gilstrap Nov. 22, 1955 

1. THE PROCESS FOR ACCELERATING THE GROWTH OF MONOCRYSTALS, WHICH COMPRISES IMPINGING ON A SELECTED FACE OF CRYSTAL A PLURALITY OF SPACED NOURSHING JETS OF A SATURATED SOLUTION SO THAT THE JETS UPON STRIKING THE CRYSTAL FACE SPREAD OUT AND MERGE TO FORM A PLURALITY OF REVERSELY DIRECTED JETS OF IMPROVERISHED SOLUTION, AND ASPIRATING SAID REVERSELY DIRECTED JETS BEFORE THEY INTERFERE WITH SAID NOURISHING JETS. 